Method of manufacturing a laminated metal sheet for packaging applications and laminated metal sheet for packaging applications made thereby

Abstract

The present invention relates to a method for manufacturing laminated metal sheets for packaging applications and the laminated metal sheets for packaging applications thus obtained.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing laminated metal sheets for packaging applications and the laminated metal sheets for packaging applications thus obtained. Background Technology

[0002] Laminated metal sheets for packaging comprise a metal sheet and a laminate covering at least one side of the metal sheet. Such laminated metal sheets are manufactured by laminating the laminate onto the metal sheet. If the laminate at least partially comprises polyester, it is applied to the metal sheet by i) thermally bonding the laminate to the metal sheet, ii) using an adhesion promoter between the laminate and the metal sheet, or iii) using a laminate containing an adhesive layer. The laminate can be manufactured in-line and laminated onto the metal sheet in an integrated lamination step, or a pre-fabricated laminate can be laminated onto the metal sheet in a separate lamination process step.

[0003] Before being laminated onto a metal sheet, the manner in which the laminate is manufactured means that most (if not all) of it is produced by stretching a thick cast film into a thin laminate, typically followed by an annealing (heat setting) stage to prevent shrinkage of the laminate during lamination onto the metal sheet. In most stretched laminates, the polymer molecules are biaxially or uniaxially oriented, depending on whether the film is biaxially or uniaxially stretched. Heat setting is particularly important if the laminate is stretched laterally.

[0004] The most commonly used laminates are biaxially stretched (or biaxially oriented (BO)), where the laminate has a similar degree of orientation in the machine direction (MD) and in the direction perpendicular to the machine direction (cross direction or transverse direction (TD)). Examples of BO laminates based on semi-crystalline polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) and their blends, laminated on a metal substrate, are disclosed in EP0312304. In most cases, the BO laminate is stretched to the same degree in both the machine direction (MD) and the transverse direction. This typically results in a more in-plane uniform orientation of the polymer chains in the material.

[0005] Another type of stretched laminate is the uniaxial stretching disclosed in US9346254B2. Machine-oriented (MDO) laminates are provided on one or both sides of a metal substrate. Without heat setting, this uniaxial stretching results in a laminate that maintains a strong orientation of the polymer chains in the stretching direction. The laminate can also be uniaxially stretched in the transverse (TDO) direction, resulting in a strong orientation of the polymer chains in the transverse direction. In both MDO and TDO laminates, the properties of the laminate differ in the two in-plane directions (MD and TD).

[0006] One drawback of using MDO laminates without heat setting is that MDO laminates are less stable in terms of wrinkling and shrinkage during the lamination process compared to heat-set uniaxial or BO laminates. On the other hand, heat-set laminates are more expensive, and they are only available as pre-prepared films. Therefore, integrating the lamination process with laminate production is impractical in this context. Equipment for producing heat-set BO laminates based on polyesters (such as PET or PBT and their blends) requires significant capital expenditure and is inflexible in terms of changes to laminate composition or formulation.

[0007] At least at the surface of the metal substrate, thermally bonding the laminate to the heated metal sheet reduces or eliminates residual orientation by remelting the laminate. It is known that if residual orientation is not sufficiently reduced, the formability, corrosion resistance, and appearance of the laminate are inadequate. Therefore, evaluating the residual orientation of the laminates on the laminate is crucial to ensuring that laminates of good quality are delivered to consumers.

[0008] Common procedures for examining residual orientation in laminates include tensile strength measurement (WO1997030841), birefringence (US5753328), and wide-angle X-ray scattering (WAXS) (JP2011008170). These methods are only suitable for analyzing laminates after the laminate has been removed from the sheet metal on which the laminate is stacked by dissolving the sheet metal.

[0009] Therefore, these methods are unsuitable for analyzing laminated metal sheets as products. Furthermore, due to the sensitivity of birefringence to polymer crystallite size, birefringence is only suitable for evaluating transparent films, which may lead to reproducibility issues. Polarized Raman spectroscopy can be used to evaluate semi-crystalline polymers on laminated metal sheets (US20160257099). However, due to scattering issues, the use of polarized Raman on semi-crystalline polymers is only suitable for quality control of transparent (uncolored) polymer films / coatings (Technical Note AN-922, 2001, WMDoyle, Axiom Analytical). In addition, these methods are very time-consuming, requiring days or even weeks to complete and extensive sample preparation. These durations and preparation efforts are incompatible with continuous production lines, as evaluation results are only available long after the laminated metal sheet production process is complete. Consequently, there is no rapid response in identifying undesirable residual orientations, which may result in a large number of scraps.

[0010] Purpose of the invention

[0011] The object of the present invention is to provide a method for manufacturing a laminated metal sheet having a controlled low residual orientation or no residual orientation in the laminated layers.

[0012] Another object of the present invention is to provide a method for manufacturing a laminated metal sheet having low or no residual orientation in the laminated layers and having a reduced amount of scrap.

[0013] Another object of the present invention is to provide a method for rapidly determining residual orientation degree to reduce the amount of waste.

[0014] Another object of the present invention is to provide a laminated metal sheet with low orientation. Summary of the Invention

[0015] In a first aspect of the invention, one or more of the above-mentioned objectives are achieved by a method of manufacturing a laminated metal sheet (9) for packaging applications, the laminated metal sheet comprising a metal sheet (1) and a laminated layer (3a) covering at least one side of the metal sheet, wherein the laminated layer (3a) contains a single layer comprising 50% by mass or more of polyester, or multiple layers (3a', 3a'', 3a'') each comprising 50% by mass or more of polyester, wherein the laminated layer (3a) has a preferred molecular orientation in one direction before being laminated onto the metal sheet (1), and wherein the first and second ATR-FTIR spectra of the laminated layer (3a) are... The Euclidean distance matrix D between them has a value of at least 0.20 (i.e., greater than 0.20), and the stacked layer has a value of less than 0.10 between the first and second ATR-FTIR spectra of the stacked layer (3a) after being stacked onto the metal sheet, and the first spectrum is measured in an ATR-FTIR spectrometer with an incident IR beam parallel or perpendicular to the machine direction of the stacked metal sheet, and the second spectrum is measured in the spectrometer after the stacked metal sheet is rotated in the stacked layer plane by an angle α selected from 70 to 110°, and the ATR-FTIR spectrum includes a range of 1160 to 1520 cm⁻¹. -1 It was measured within the spectral range.

[0016] WO2017102143 discloses a method for laminating a polyester film onto the main surface of a metal strip in a coating line, with an emphasis on preventing wrinkles and creases in the polyester film during the lamination process by selecting an appropriate combination of film tension, linear velocity, and yield stress of the polyester film.

[0017] WO2019110616 discloses a method for manufacturing polymer-coated steel sheets for three-piece cans by laminating multiple narrow polymer strips onto tinplate.

[0018] Both WO2017102143 and WO2019110616 disclose a post-heating step after lamination, intended to obtain low-crystallinity or amorphous polymer films after lamination, but neither discloses a method for rapidly determining the crystallinity level. They only vaguely mention time-consuming offline methods such as X-ray diffraction, density measurement, and DSC.

[0019] Since the Euclidean distance matrix D between the first and second ATR-FTIR spectra depends on the choice of angle α, this angle α must be chosen within the required range, and the same angle must be used when comparing the first and second ATR-FTIR spectra of the stacked layers to obtain comparable and definitive results.

[0020] The machine orientation (MD) of the laminated metal sheet is the same as the rolling orientation (RD) of the metal sheet and the same as the direction of movement of the metal sheet during the lamination process.

[0021] Preferably, the first spectrum is measured with an orientation in the machine direction, and the second spectrum is measured after rotation by an angle selected from 70 to 110°. Alternatively, the first spectrum is measured with an orientation perpendicular to the machine direction, and the second spectrum is measured after rotation by an angle selected from 70 to 110°.

[0022] A D value of 0 means that the first and second spectra overlap within the observed range and there is no difference in orientation in the polymer coating in both directions. A D value greater than 0 indicates the presence of residual orientation in the laminate. An acceptable level of D of at most 0.10 (i.e., below 0.10) is determined based on a reference sample. When the D value is 0.20, there is a significant difference between the two spectra, meaning that the orientation of the polymer chains in the laminate differs in both directions. At D values ​​of at least 0.30 or even 0.40, this difference becomes increasingly pronounced, and therefore the difference in orientation becomes more significant.

[0023] This invention is suitable for cases where the laminate has different orientations in the rolling direction and transverse direction (TD) before being laminated onto a metal sheet. If the orientations in both directions are the same before lamination, then D may be lower before lamination. This is the case for biaxially oriented laminates that have been stretched to the same degree in RD and TD, and for extruded laminates that are laminated directly onto the metal without intermediate solidification and stretching.

[0024] The present invention is particularly suitable for cases in which the laminate is stretched only in the machine direction or only in the transverse direction.

[0025] Preferred embodiments are provided by dependent claims 2 to 14.

[0026] This invention is embodied in a method for manufacturing laminated metal sheets in a continuous coating line, the method comprising the following sequential steps:

[0027] • Provide metal sheets;

[0028] • Provide a laminate (3a) for coating onto at least one side of a metal sheet, having an Euclidean distance matrix D between a first and a second ATR FTIR spectrum of the laminate (3a) of 0.20 or more;

[0029] • The laminate (3a) is laminated onto the metal sheet (1) to manufacture the laminated metal sheet (9);

[0030] • The laminated metal sheet (9) is then heated to a temperature high enough to melt the laminate (3a);

[0031] • Cooling, preferably rapid cooling of the post-heated laminated metal sheet (9) to produce a laminated metal sheet (9) having an Euclidean distance matrix D of less than 0.10 between the first and second ATR FTIR spectra of the laminated layer (3a).

[0032] In a preferred embodiment, the laminate for coating onto the metal sheet comprises one or more layers and is provided by the following method:

[0033] - Melting thermoplastic polymer particles in one or more extruders to form one or more layers;

[0034] - A thermoplastic polymer film consisting of two or more layers is formed by passing molten polymer through a flat (co)extrusion die and / or two or more calendering rolls;

[0035] Optional:

[0036] - Cool the thermoplastic polymer film to form a solid thermoplastic polymer film;

[0037] -Optional trimming of the edges of the thermoplastic polymer film;

[0038] - The thickness of the solid thermoplastic polymer film is reduced by stretching the solid polymer film in the stretching unit by applying a tensile force only in the longitudinal direction;

[0039] -Optional trimming of the edges of the stretched thermoplastic polymer film.

[0040] In one embodiment, the method of the present invention is used to adjust one or both of the process parameters of a continuous coating line, such as the post-heating setpoint (T2) and line speed (v), if the Euclidean distance matrix D of the stacked layers exceeds 0.10 after post-heating and cooling. Once D exceeds this threshold, the orientation is too large, and the product may perform poorly, which may lead to the material being rejected or downgraded to a lower-value product. The speed of the method of the present invention ensures a significant reduction in the amount of scrap compared to the prior art.

[0041] In one embodiment, the metal sheet is a steel sheet, preferably uncoated cold-rolled steel, tinplate, ECCS (aka TFS), TCCT, galvanized steel, or aluminized steel, and preferably the thermoplastic polymer film is a single-layer or multi-layer polyester or polyolefin polymer film.

[0042] In one embodiment, the one or more thermoplastic polymer films are biaxially oriented polymer films.

[0043] In one embodiment, the one or more thermoplastic polymer films are uniaxially oriented polymer films.

[0044] In a preferred embodiment, the laminate is stacked onto a metal sheet to continuously manufacture the laminated metal sheet during the continuous stacking process.

[0045] A method for online monitoring of residual orientation in the polymer coating of laminated metal sheets obtained by laminating uniaxially or biaxially oriented polyester films includes the following steps:

[0046] a. Obtain a sample of the laminated metal sheet;

[0047] b. Place the sample on the ATR detector of the ATR-FTIR spectrometer, such that the rolling direction of the laminated metal sheet is parallel to the incident plane of the incident light from the infrared source of the spectrometer to the ATR crystal.

[0048] c. At least 1160-1520cm -1 Record the reflectivity distribution within the frequency range;

[0049] d. Use Fourier transform to generate the first ATR-FTIR spectrum of the sample within this frequency range;

[0050] e. Rotate the sample of the stacked metal sheet in a plane perpendicular to the normal of the sample surface at an angle α of 70 to 110°, and repeat steps c and d to generate a second ATR-FTIR spectrum;

[0051] f. By calculating the spectral distance as represented in the Euclidean distance matrix D between the two spectra, a mathematical comparison shows that the distance is at least 1160-1520 cm. -1 Correlation between the first and second spectra within the frequency range.

[0052] A D value of 0 means that the first and second spectra overlap within the observed range and there is no difference in orientation of the polymer coating in both directions. A D value greater than 0 indicates the presence of residual orientation in the laminate. An acceptable level of D of up to 0.10 is determined based on a reference sample. When the D value is 0.20, there is a significant difference between the two spectra, meaning that the orientation of the polymer chains in the laminate differs in both directions.

[0053] In attenuated total reflectance infrared spectroscopy (ATR-FTIR), a material with a lower refractive index (the sample) is brought into contact with a material with a higher refractive index (such as germanium or diamond crystals). Mid-infrared light irradiated through the higher refractive index material undergoes total internal reflection at the interface between the two materials. The reflected IR light is then collected by an IR detector and mathematically processed by Fourier transform to obtain the ATR-FTIR spectrum. This ATR-FTIR spectrum contains highly characteristic and reproducible bands that can be directly assigned to a specific chemical composition (e.g., using an FTIR database), thus providing information about the chemical composition of the surface layer of the material (typically 1-2 μm). The IR light is at least partially polarized before entering the sample (using an additional polarizer or simply after passing through the higher refractive index material). Due to the polarization of the IR light, its interaction with the molecular dipoles of the polymer depends on the orientation of the polymer molecules. If a residual orientation exists in the stacked layers, the spectrum depends on the angle between the ATR crystal and the sample. When the sample does not have a residual orientation, the ATR-FTIR spectrum appears independent of the angle between the ATR crystal and the sample.

[0054] By irradiating a laminated metal sheet with partially polarized infrared light and subsequently collecting and analyzing the reflected infrared light, such as in the case of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), several limitations in measuring residual orientation in existing techniques are overcome. This method utilizes the dichroic IR band in the ATR-FTIR spectrum, which serves as one of the components used as orientation markers. The intensity of the dichroic IR band is highly dependent on the orientation of the polymer chains relative to the incident polarized infrared light. The degree of orientation can be assessed by comparing, for example, the intensity of the dichroic IR band in two directions relative to the IR detector of the laminated metal sheet. For isotropic laminates, the intensity of the dichroic band is the same at all locations of the laminated metal sheet relative to the IR detector. Typically, the intensity of the dichroic IR band is normalized to the intensity of certain non-dichroic IR bands to compensate for sample surface defects, etc. In the case where the polymer coating contains polyethylene terephthalate (PET) and its blends, the degree of orientation is typically assessed by following the trans (1340 cm⁻¹) distribution of the CH₂ moiety of PET. -1 JP2003127307) or adjacent intersection (1043cm) -1 The intensity of the dichroic peak in the form of JP2002160721 was then normalized to 1410 cm⁻¹. -1The non-dichroic IR bands at the location (in-plane bending vibrations of the benzene rings in PET). The limitation of this method is that it assesses the overall surface orientation of semi-crystalline polymer blends based on the behavior of only one component (an orientation marker)—in this case, PET—rather than the behavior of the entire polyester blend. Furthermore, this method is highly dependent on the presence of fully resolved dichroic IR bands—which is not always the case, as in many cases the IR bands are a superposition of several separate bands. Therefore, the analysis of each new blend of polyester, if not based on PET or containing very little PET, may require entirely different dichroic IR bands. A simple analysis of the intensity of the dichroic IR bands also ignores variations in the shape or spectral position of the dichroic IR bands relative to different locations on the ATR-FTIR spectrometer.

[0055] These problems are overcome by the method of the present invention, which involves irradiating and collecting partially reflected polarized infrared light, such as in the case of attenuated total reflection Fourier transform infrared spectrometer (ATR FTIR).

[0056] The inventors discovered that the orientation of a semi-crystalline blend laminated on a metal sheet can be determined by comparing two ATR-FTIR spectra measured in two different directions within a specific frequency range, including but not limited to 1160 to 1520 cm⁻¹, of a laminated metal sheet sample rotated at a set angle relative to the sample normal. -1 scope.

[0057] The preferred frequency range is 1160 to 1520 cm⁻¹ -1 The rotation angle α between the two directions of the sample is preferably about 90°. The advantage of this method, which assesses residual orientation based on measuring two ATR-FTIR spectra, is that it can be applied to a wide range of copolymers, including PET and / or PBT-based polyesters, copolyesters, and blends. This method provides information similar to birefringence measurements, but its advantage lies in its ability to be performed on laminated metal sheets, regardless of the size of the polymer crystallites. Furthermore, this method considers not only the variations in IR band intensity of polymer-coated samples with different orientations, but also the influence of sample position on the shape or spectral position (shift) of various IR bands.

[0058] The laminated metal sheet of the present invention may have laminated layers on one or both sides of the metal sheet. In the latter case, the laminated layer ( Figure 1 3a and 3b) in the text may be the same in terms of composition, thickness or construction, or they may be different.

[0059] In one embodiment, the laminated metal sheet of the present invention has an Euclidean distance matrix D between two ATR-FTIR spectra of the laminated layer of 0.00 to 0.07. The smaller the value of D, the smaller the difference between the two spectra, and thus the smaller the degree of orientation in the laminated layer. In a preferred embodiment, the Euclidean distance matrix D between the two ATR-FTIR spectra of the laminated layer is 0.00 to 0.05, and even more preferably D is at most 0.03.

[0060] The laminate of the present invention is a thermoplastic single-layer / multi-layer semi-crystalline oriented film comprising at least 50% polyester. The laminate preferably comprises semi-crystalline polyester or polyester blends, particularly those based on PET, PETg, IPA-PET, CHDM-PET, and PBT (in any ratio). Preferably, the total amount of polyester in the laminate is at least 60%. More preferably, this amount is at least 70%, more preferably at least 80%, even more preferably at least 90%, or even at least 95%.

[0061] The metal sheet is selected from metal sheets such as cold-rolled steel, black steel plate, tinplate, ECCS, etc. Galvanized steel, aluminum, or aluminum alloy. The sheet metal is preferably supplied in wound form. The laminated sheet metal is also preferably supplied in wound form, although it can be supplied to consumers in sheet or blank form.

[0062] In one embodiment, the laminate is applied at least to the side of the metal sheet that becomes the inside of the packaging (such as a container or can), and the polyester in the laminate contains at least 70 mol% of polyethylene terephthalate units. Preferably, the laminate contains at least 80 mol% or even 85 mol% of polyethylene terephthalate units.

[0063] In one embodiment, the laminate is applied at least to the side of the metal sheet that becomes the inside of the packaging (such as a container or can), and the polyester in the laminate contains at least 85 mol% butylene terephthalate units.

[0064] In one embodiment, the laminate is applied at least to the side of the metal sheet that becomes the inside of the packaging (such as a container or can), and the polyester in the laminate contains a blend of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), preferably wherein the ratio of PET to PBT is 60:40 or more. Preferably, the ratio is 70:30.

[0065] In one embodiment, the laminate is applied at least to the side of the metal sheet that becomes the inside of the packaging (such as a container or can), and the polyester in the laminate contains at least 85 mol% of a blend of polyester containing 85 mol% ethylene terephthalate units and polyester containing at least 85 mol% butylene terephthalate units.

[0066] According to a second aspect of the invention, a laminated metal sheet for packaging applications according to the invention is provided in claim 15. Example

[0067] To illustrate the invention, a laminated metal sheet was manufactured. In all cases, a thermoplastic polymer laminate is provided on both sides of the metal sheet. The metal sheet is a low-carbon cold-rolled packaging steel, commonly known as electrolytically chromium-plated steel (“ECCS”), which is electroplated with metallic chromium and a layer of chromium oxide on both sides, wherein the total amount of chromium on each side is approximately 90 mg / m². 2 .

[0068] The polyester films in Table 1 were used to manufacture comparative and test samples.

[0069] Table 1: Layer Stack

[0070]

[0071] PETg=Eastman Eastar 6763, IPA-PET=Indorama Ramapet N180, TiO2 MB=Sukano TA 76-98MB03), PBT=Sabic Innovative Plastics Valox 315).

[0072] pass Figure 1 The thermal bonding process illustrated in the diagram laminates films PET1 to PET6 onto ECCS strips. The metal strip (1) passes through a first heating device (2), where the temperature of the metal strip rises to a preheating temperature T1 suitable for lamination. Simultaneously, film rolls (3a, 3b) unfold and pass through a pair of lamination rollers (4a, 4b) together with the preheated metal strip. The laminated product (5) passes through a second heating device (6), where the temperature of the laminated strip rises to a post-heating temperature T2. Immediately after the second heating device, the laminated product passes through a quenching device (7) to cool to room temperature. The method of preheating the metal strip in the first heating device is not particularly limited and may include passing the strip through heated rollers, conductive heating, induction heating, radiant heating, etc. The method of post-heating the laminated product in the second heating device is preferably a non-contact method, such as heating in a hot air environment or induction heating. The method of immediate cooling in the quenching device is not particularly limited and may include applying cold air or passing through a cold water bath, etc. The laminated product then passes through drying rollers (8a, 8b), and samples are subsequently collected to obtain ATR-FTIR profiles on the samples.

[0073] Table 2 details the comparative samples (“CS”) and test samples (“TS”) prepared to demonstrate the applicability of the ATR-FTIR method for measuring the residual orientation of various polyester film compositions. Table 2 also details the corresponding process conditions used to obtain these samples. In the case of the TS3 sample, due to delamination during the process, it was impossible to prepare the corresponding comparative sample without a post-heating temperature or with a low post-heating temperature, and the TS3 data are compared with those obtained for PET5 films before lamination.

[0074] Table 2: Process conditions for manufacturing comparative and inventive samples

[0075]

[0076] After sample production, ATR-FTIR spectra were recorded, and the spectral distance D was derived from the sides of the MDO films (PET1, PET3, PET4, PET5). Based on the obtained spectral distance D, the metal laminates were classified as good and poor quality as described below. The classification results obtained by ATR-FTIR on polymer-coated metal strips were then compared with product performance test results and DSC, as well as tensile strength measurements on PET5 films or self-supporting laminates (after metal removal with hydrochloric acid).

[0077] The laminated metal sheet sample was cut into 7.5 × 7.5 cm plates. ATR-FTIR spectra were recorded using a Bruker Tensor II ATR-FTIR spectrometer equipped with a diamond crystal at a fixed predetermined incident angle of 45°. The spectra were observed at 1160–1520 cm⁻¹. -1 Apply 0.4cm -1 The ATR-FTIR signal was recorded using 16 scans at a resolution of [resolution missing]. Background signals were recorded before recording the actual ATR-FTIR spectra. For the TS3 sample, compared with data from a PET5 film (since a corresponding insufficiently post-heated film was not prepared), the ATR-FTIR spectrum was recorded using a Thermo Scientific Nicolet 650iS10 ATR-FTIR spectrometer equipped with a ZnSe crystal at a fixed predetermined incident angle of 42°. In this case, the [resolution missing] was also [resolution missing]. -1 Eight scans were collected at a resolution of [resolution value].

[0078] For each sample, two spectra were recorded: spectrum 1 was recorded with respect to the sample rolling direction (which is the same as the machine direction (MD) of the continuous coating line) perpendicular to the incident plane from the infrared source of the spectrometer onto the ATR crystal, and spectrum 2 was recorded after rotating the metal laminate sample by 90° in the sample plane.

[0079] Mathematical comparison of spectra 1 and 2 via 1160 to 1520 cm⁻¹ -1 The spectral distance D is calculated within the spectral range after vector normalization (to compensate for intensity differences caused by surface defects). The calculated spectral distance D is the Euclidean distance matrix between the two spectra. The calculated Euclidean distance matrix can fall within the range of 0 (perfect spectral match) to 2 (perfect spectral mismatch). As a threshold, D = 0.10 is determined by comparing the results of known good and bad samples.

[0080] D is calculated using the following formula:

[0081]

[0082] Where a(k) and b(k) are the ordinate values ​​of the spectra of a and b, respectively. The sum is incorporated into all selected k data points. Figure 2 A schematic example of two curves is shown. The spectral distance D is proportional to the gray area between the two sine curves.

[0083] Before the spectral distance D can be determined, the data must be preprocessed. Thus, the value of D falls between 0 (equal spectra) and 2 (maximum inequality between spectra). This preprocessing is a normalization method that first calculates the average y-value of the spectrum, using only data points within the selected spectral range. The calculated average is then subtracted from the spectrum, resulting in a spectrum centered at y=0. The sum of the squares of all y-values ​​is then calculated, and the corresponding spectrum is divided by the square root of this sum. The resulting spectrum has a vector norm of 1.

[0084]

[0085] a′(k)=a(k)-a m

[0086]

[0087]

[0088] If the normalized spectrum is represented in n-dimensional space, where n is the number of selected data points, then all spectra lie on a unit sphere (an n-dimensional sphere with radius 1 surrounding the origin). The maximum distance between two spectra is the diameter of the unit sphere, i.e., (D = )². The minimum distance is when all points of the two spectra overlap on the unit sphere, i.e., D = 0.

[0089] The thermal properties of the polymer film (Tg, Tm, orientation-induced crystallinity) were determined by DSC. The spectra were recorded using a Mettler Toledo DSC821e instrument operating at a heating rate of 10 °C / min. For DSC, it was necessary to analyze the self-supporting film obtained from the laminated metal sheet. The self-supporting polymer film was obtained by placing a sample of the metal laminate from the production line in an 18% hydrochloric acid aqueous solution to dissolve the metal substrate. After the metal substrate was dissolved, the polymer film was thoroughly rinsed and dried. The crystallinity fraction was determined by the recrystallization heat and the thermal melting recorded during the first heating run, as described in detail elsewhere. The orientation-induced crystallinity value was calculated by the following ratio:

[0090]

[0091] Where ΔH r It is the area of ​​the observed recrystallization peak, and ΔH m The area of ​​the observed melting peak is given, and ΔH0 is assumed to be the enthalpy of fusion of 100% crystalline PET at 115.0 J / g (J. Brandrup, E. Himmergut, E. A. Gruike et al., Polymer Handbook, Wiley Interscience, 4th ed. (1999), Chapter VI, Table 7), and the ΔH0 for crystalline PBT is assumed to be the same as that for crystalline PET. Fully remelted non-oriented PET and PBT polymers in laminated metal sheets have crystallinity values ​​below 10%.

[0092] The mechanical properties of polymer films after metal removal were determined using a Shimadzu EZ-LX tensile testing machine, which features a single-column main unit with a stroke length of 920 mm, pneumatic clamps, and a 500 N force gauge. Tensile tests were performed according to ISO 527. For this test, strips 15 mm wide and 150 mm long were cut from the self-supporting polymer film. To measure the tensile properties of the film in the machine direction, a single test speed of 50 mm / min was used from the start to the end (film breakage). For measuring the transverse tensile properties of the film, a dual-speed scheme was applied, where an elongation of 60 mm was applied from the start at 50 mm / min, and then the test speed was increased to 500 mm / min until the breakage point. The difference in speed schemes between the machine direction and the transverse direction is because the tensile strain and elongation at break can be much higher in the transverse direction than in the machine direction. All tests were performed ten times for each polymer film, and then outliers were excluded to achieve a maximum modulus change of 10%. The modulus value was then averaged. Orientation is assessed by comparing the modulus (in MPa) in the machine orientation and transverse direction of the sample.

[0093] For this test, a 7.5 × 7.5 cm plate was cut from the flat sheet. The plate was then placed in a sealed container in an aqueous solution containing 12 g / L Maggi + 2 g / L plasmal and subsequently sterilized at 121°C for 90 minutes (for samples TS1, TS2, CS1, and CS2). For TS3, the sample was sterilized in water at 121°C for 90 minutes. After sterilization and cooling, 4 × 5 mm cross-lacing lines were applied to the flat portion of the plate according to the method described in ISO 2409:1992, 2nd edition, followed by adhesive tape. Delamination was then evaluated using a Gitterschnitt rating from 0 (excellent) to 5 (poor) (Table 3). All tests were performed three times on each side for each metal laminate variant in Table 2. The scores of the three results were then averaged and rounded to the nearest integer.

[0094] Table 3: Classification of Gitterschnitt Results

[0095]

[0096] Table 4 summarizes all characterization data for the test and comparison samples. Subsequently, the characterization data of the self-supporting film, as well as the adhesion and sterilization data on the metal-laminated samples, were compared with the spectral distance values ​​D obtained by comparing the ATR-FTIR spectra 1 and 2 of the corresponding metal laminates or PET5.

[0097] As shown in Table 4, post-heating of the metal laminate TS1 at T2 = 260°C, TS2 at T2 = 270°C, and TS3 at T2 = 275°C yielded completely unoriented isotropic polymer coatings, where the uniaxial orientation in the machine direction and residual orientations (present in PET1, PET3, PET4, and PET5 before lamination) were removed. In the case of the PET-based coating, the coating was also additionally completely amorphous, as indicated by the low crystallinity values ​​obtained by DSC (below 10% in all cases). The unoriented isotropic nature of these polymer films was confirmed by measuring their mechanical properties. In particular, the free polymer films obtained from the top sides of TS1 and TS3 and the sides of TS2 showed similar modulus values ​​in both the mechanical and transverse directions. The properties of the sides coated with PET1, PET3, and PET4 were excellent in the adhesion and sterilization tests (Gitterschnitt) (affected cross-sectional area less than 5%). The Gitterschnitt test data are consistent with the mechanical properties of fully remelted isotropic and amorphous PET coatings and free-coating films, as confirmed by DSC. Samples TS1 to TS3 are therefore classified as samples of good quality.

[0098] In contrast, post-heating of the metal laminate CS1 at T2 = 200°C and shutting off post-heating in the case of manufacturing the metal laminate CS2 resulted in incompletely remelted semi-crystalline polymer coatings, in which the uniaxial orientation in the machine direction was retained (present in PET1, PET3, and PET4 before lamination). Attempts to laminate PET5 at post-heating temperatures below 275°C to manufacture CS3 resulted in complete delamination of the PET5 laminate during processing. The high crystallinity values ​​obtained by DSC demonstrate the high crystallinity of the incompletely remelted comparative samples (above 30% in all cases). Measurements of their mechanical properties demonstrate the presence of preferred orientation in these polymer-coated films. In particular, the modulus values ​​measured before lamination for the polymer coatings or PET5 films from CS1 and CS2 were 2 (top side in CS1 and CS2), 2.6 (bottom side in CS2), and 1.4 (PET5) higher in the machine direction than those in the transverse direction. Films from CS1 (top side) and CS2 (top and bottom sides) coated with PET1, PET3, and PET4 exhibited poor performance in adhesion and sterilization tests, affecting 5-15% (TS1 top side) and 65-100% (TS2) of the cross-sectional area. The Gitterschnitt test data for the metal laminate samples CS1 and CS2 were consistent with the development of crystallinity and residual orientation in the polyester coatings of these samples. Therefore, CS1 and CS2 samples were classified as substandard.

[0099] For the comparative samples TS1 (top side), TS2 (top and bottom sides), CS1 (top side), and CS2 (top and bottom sides), DSC data and the mechanical strength of the free polymer coating film, as well as the adhesion and sterilization data of the metal stack, were compared with the corresponding spectral distance values ​​D. The D values ​​were calculated by comparing 1160–1520 cm⁻¹ directly recorded on the metal stack sample or PET5 before lamination. -1 The D values ​​were obtained from ATR-FTIR spectra 1 and 2 in the spectral regions. As shown in Table 4, the D values ​​(0.010) of the fully remelted isotropic comparison samples TS1 (top side) (0.016), TS2 (top side) (0.046), TS2 (bottom side) (0.006), and TS3 (top side) are close to 0, corresponding to fully post-heated isotropic non-oriented coatings as measured by ATR-FTIR. Conversely, the D values ​​of the machine-oriented PET5 film (0.424), and the incompletely remelted test samples CS1 (top side) (0.482), CS2 (top side) (0.480), and CS2 (bottom side) (0.482) are much higher than 0, corresponding to oriented coatings with preferred orientation in one direction, consistent with the DSC data and mechanical property studies of these samples. As a threshold, a D value of 0.10 can be used to distinguish between samples of poor and good quality.

[0100] Overview of the attached figures

[0101] The invention will now be explained with the aid of the following non-limiting drawings.

[0102] Figure 1 A schematic diagram of an industrial continuous coating production line is shown.

[0103] Figure 2 A schematic diagram showing the distance between the two spectra is displayed.

[0104] Figure 3 Spectrum CS1 – Undesirable sample on the top side.

[0105] Figure 4 Spectrum TS1 – Good sample on the top side.

[0106] Figure 5 Spectrum CS2 – Undesirable sample on the top side.

[0107] Figure 6 Spectrum TS2 – Good sample on the top side.

[0108] Figure 7 Spectrum CS2 – Poor sample on the bottom side.

[0109] Figure 8 Good sample with spectral TS2 – bottom side.

[0110] Figure 9 PET5 film with machine orientation before spectral stacking.

[0111] Figure 10 Spectrum TS3 – Good sample on the top side.

[0112] Figure 11 Construction of laminated metal sheets.

[0113] Figure 12 An illustrative explanation of the method of the present invention.

[0114] pass Figure 1The method schematically shown in the diagram involves stacking the layers onto a metal strip. The metal strip (1) passes through a first heating device (2), wherein the temperature of the metal strip rises to a preheating temperature T1 suitable for stacking. In this embodiment, T1 is selected as 200°C for stacking pure PET film, 220°C for stacking film containing 25% PBT, and 225°C for stacking film based on pure PBT. Rolls of films PET1, PET3, or PET5 (3a) and PET2, PET4, or PET6 (3b) are simultaneously unrolled and passed through a pair of stacking rollers (4a, 4b) along with the preheated metal strip. The stacked metal sheet (5) passes through a second heating device (6), wherein the temperature of the stacked metal sheet rises to a post-heating setpoint T2. After the second heating device, the stacked metal sheet is immediately cooled to room temperature by passing through a quenching device (7). There are no particular limitations on the method of preheating the metal strip in the first heating device, and it can include passing the strip through heated rollers, conduction heating, induction heating, radiation heating, etc. The method of post-heating the laminated metal sheets in the second heating device is preferably a non-contact method, such as heating in a hot gas environment or induction heating. There are no particular limitations on the method of immediate cooling in the quenching device, and it can include applying cold air or passing the strip through a cold water bath, etc.

[0115] The spectral distance D is proportional to the region between the two curves. Figure 2 The image depicts two model sine curves. The spectral distance is proportional to the gray area between the two sine curves.

[0116] Figure 11 A schematic construction of a laminated metal sheet is shown. The upper figure shows the simplest form of the laminated metal sheet 9, where the metal sheet 1 has a laminated layer 3a. The lower figure shows a more complex embodiment according to the invention, where the metal sheet 1 has multiple laminated layers 3a on top, wherein the multiple layers (in this embodiment) comprise three separate layers 3a', 3a”, and 3a”’, for example, acting as a top layer, a body layer, and an adhesive layer, respectively, each layer possibly having a different composition tailored to the requirements of the individual layers, and a second laminated layer on the bottom of the metal sheet, which, in the case of a symmetrical laminated metal sheet, is the same as the laminated layer on top in terms of composition, construction, or thickness, or different in the case of an asymmetrical laminated metal sheet.

[0117] Figure 12A schematic explanation of the preparation of a sample taken from a laminated metal sheet and subsequent measurements in an ATR-FTIR spectrometer is shown. The first spectrum was measured with an incident IR beam parallel to the machine direction (MD)—which is the same as the rolling direction (RD)—and the second spectrum was measured with an incident IR beam more or less perpendicular to the machine direction (rotation angle α). The Euclidean distance matrix D was determined between these two spectra, and after post-heating and cooling, the value of D according to the invention is at most 0.10.

[0118]

Claims

1. A method for manufacturing a laminated metal sheet (9) in a continuous coating line operating at a linear speed v, the laminated metal sheet (9) comprising a laminated layer (3a), the method comprising the following sequential steps: • Provide metal sheets (1); A laminate (3a) is provided for coating onto at least one side of a metal sheet, having a value of 0.20 or greater for the Euclidean distance matrix D between a first ATR FTIR spectrum and a second ATR FTIR spectrum in the laminate (3a), wherein the first ATR FTIR spectrum is measured in an ATR-FTIR spectrometer with an incident IR beam parallel or perpendicular to the machine direction of the laminated metal sheet, and wherein the second ATR FTIR spectrum is measured in the spectrometer after the laminated metal sheet is rotated in the plane of the laminate by an angle α selected from 70 to 110°, and wherein the first ATR-FTIR spectrum and the second ATR FTIR spectrum are within a range of 1160 to 1520 cm⁻¹. -1 Measured within the spectral range of the range; • The laminate (3a) is laminated onto the metal sheet (1) to manufacture the laminated metal sheet (9); • The laminated metal sheet (9) is then heated to a post-heating setpoint T2 high enough to melt the laminated layer (3a); • Rapidly cooling the post-heated laminated metal sheet (9) to produce a laminated metal sheet (9) having an Euclidean distance matrix D between a first ATR FTIR spectrum and a second ATR FTIR spectrum of the laminated layer (3a) with a value of less than 0.10, wherein the first ATR FTIR spectrum is measured in an ATR-FTIR spectrometer with an incident IR beam parallel or perpendicular to the machine direction of the laminated metal sheet, and wherein the second ATR FTIR spectrum is measured in the spectrometer after the laminated metal sheet is rotated in the laminated layer plane by an angle α selected from 70 to 110°, and wherein the first ATR FTIR spectrum and the second ATR-FTIR spectrum are within a range of 1160 to 1520 cm⁻¹. -1 Measured within the spectral range of , The laminate consists of one or more layers, which are PET and / or PBT-based polyesters, copolyesters and blends, and each layer in the laminate contains a polyester content of greater than or equal to 67% by mass.

2. The method of claim 1, wherein the laminate is provided by a process comprising the following steps: 1) Melting thermoplastic polymer particles in one or more extruders to form one or more layers; and 2) A thermoplastic polymer film consisting of two or more layers is formed by passing molten polymer through a flat extrusion die or a flat co-extrusion die and / or two or more calendering rolls.

3. The method of claim 2, wherein the process after step 2) includes the step of: 3) Cooling the thermoplastic polymer film to form a solid thermoplastic polymer film; and -4) The thickness of the solid thermoplastic polymer film is reduced by stretching the solid thermoplastic polymer film in the stretching unit by applying a tensile force only in the longitudinal direction.

4. The method of claim 3, wherein the process after step 3) and before step 4) comprises: 3') Trim the edges of the solid thermoplastic polymer film.

5. The method of claim 3, wherein the process after step 4) comprises: -5) Trim the edges of the stretched solid thermoplastic polymer film.

6. The method of claim 3, wherein the process after step 3) and before step 4) comprises: 3') Trim the edges of the solid thermoplastic polymer film; And after step 4), it includes: -5) Trim the edges of the stretched solid thermoplastic polymer film.

7. The method of claim 1 or 2, wherein if the Euclidean distance matrix D of the stacked layers after post-heating and cooling has a value greater than 0.10, the post-heating setpoint T2 and / or the line velocity v of the continuous coating line are adjusted.

8. The method of claim 1 or 2, wherein α is selected from 80 to 100°.

9. The method of claim 1 or 2, wherein the metal sheet is steel.

10. The method of claim 2, wherein the thermoplastic polymer film is a single-layer or multi-layer polyester polymer film.

11. The method of claim 2, wherein the one or more thermoplastic polymer films are biaxially oriented polymer films.

12. The method of claim 6, wherein the one or more thermoplastic polymer films are uniaxially oriented polymer films.

13. The method of claim 1 or 2, wherein the laminates are stacked onto a metal sheet to manufacture the laminated metal sheet continuously in a continuous process.

14. The method of claim 1, wherein the laminate (3a) is applied at least to the inner side of the metal sheet that forms the package, and the polyester in each layer of the laminate contains at least 70 mol% of polyethylene terephthalate units.

15. The method of claim 1, wherein the laminate (3a) is applied at least to the inner side of the metal sheet that forms the package, and the polyester in each layer of the laminate contains at least 85 mol% of butylene terephthalate units.

16. The method of claim 1, wherein the laminate is applied at least to the inner side of the metal sheet that forms the package, and the polyester in each layer of the laminate contains a blend of polyethylene terephthalate and polybutylene terephthalate.

17. The method of claim 1, wherein the laminate is applied at least to the inner side of the metal sheet that forms the package, and the polyester in each layer of the laminate comprises a blend of at least 85 mol% of a polyester containing 85 mol% of polyethylene terephthalate units and a polyester containing at least 85 mol% of butylene terephthalate units.

18. The method of claim 1 or 2, wherein the laminate (3a) comprises a single layer containing 67% by mass or more of polyester or multiple layers each containing 67% by mass or more of polyester, wherein the laminate has a preferred molecular orientation in one direction before being laminated onto the metal sheet, and wherein the Euclidean distance matrix D between the first ATR-FTIR spectrum and the second ATR-FTIR spectrum of the laminate is 0.20 or more, and wherein the laminate has a D value of less than 0.10 between the first ATR-FTIR spectrum and the second ATR-FTIR spectrum of the laminate after being laminated onto the metal sheet.

19. The method of claim 8, wherein α is 90°.

20. The method of claim 9, wherein the steel is uncoated cold-rolled steel, tinplate, ECCS, TCCT, galvanized steel, or aluminized steel.

21. The method of any one of claims 14-17, wherein the packaging is a container.

22. The method of any one of claims 14-17, wherein the packaging is a can.

23. The method of claim 16, wherein the ratio of polyethylene terephthalate to polybutylene terephthalate is 60:40 or higher.

24. A laminated metal sheet (9) for packaging applications obtained by the method of any one of claims 1 to 23, the laminated metal sheet comprising a metal sheet (1) and a laminate (3a) covering at least one side of the metal sheet, wherein the laminate (3a) comprises one or more layers, and each layer of the laminate comprises greater than or equal to 67% by mass of polyester, wherein the laminate has a D value between a first ATR-FTIR spectrum and a second ATR-FTIR spectrum of the laminate (3a) after being laminated onto the metal sheet, and wherein the first ATR-FTIR spectrum is measured in an ATR-FTIR spectrometer with an incident IR beam parallel or perpendicular to the machine direction of the laminated metal sheet, and wherein the second ATR-FTIR spectrum is measured in the spectrometer after the laminated metal sheet is rotated in the plane of the laminate by an angle α selected from 70 to 110°, and wherein the first ATR-FTIR spectrum and the second ATR-FTIR spectrum are within a range of 1160 to 1520 cm⁻¹. -1 It was measured within the spectral range.

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